Support to Oil Spill Emergencies in the Bonifacio Strait, Western Mediterranean

Ocean Sci., 8, 443–454, 2012 www.ocean-sci.net/8/443/2012/ Ocean Science doi:10.5194/os-8-443-2012 © Author(s) 2012. CC Attribution 3.0 License.

Support to oil spill emergencies in the Bonifacio Strait, western Mediterranean

A. Cucco1, A. Ribotti1, A. Olita1, L. Fazioli1, B. Sorgente1, M. Sinerchia1, A. Satta1, A. Perilli1, M. Borghini2, K. Schroeder2,*, and R. Sorgente1 1CNR IAMC U.O.S. Oristano, Oristano, Italy 2CNR ISMAR U.O.S. La Spezia, La Spezia, Italy *now at: CNR ISMAR U.O.S. Venezia, Italy

Correspondence to: A. Ribotti ([email protected])

Received: 13 January 2012 – Published in Ocean Sci. Discuss.: 9 February 2012 Revised: 28 May 2012 – Accepted: 7 June 2012 – Published: 10 July 2012

Abstract. An innovative forecasting system of the coastal land-based installations, are estimated at 120 000 t year−1, marine circulation has been implemented in the Bonifacio thus leading to elevated oil concentrations in their vicinity Strait area, between Corsica and Sardinia, using a numerical (EEA, 2006). approach to facilitate the rapid planning and coordination of Due to its strategic position at the centre of the western remedial actions for oil spill emergencies at sea by local au- Mediterranean Sea, between Corsica and Sardinia, the Strait thorities. Downscaling and nesting techniques from regional of Bonifacio (SoB hereafter) is annually crossed by an aver- to coastal scale and a 3-D hydrodynamic numerical model, age of 3500 vessels, mainly solid bulk cargo ships and roll coupled with a wind wave model, are the core of the inte- on/roll off passengers (Ro/Pax), with a gross tonnage rang- grated Bonifacio Strait system. Such a system is capable of ing between 500 and 25 000 t (Sorgente et al., 2012), as cal- predicting operationally the dispersion of hydrocarbon spills culated from 2000–2009 data acquired by the local vessel in the area, both in forward and backward mode, through an traffic service named Bonifacio Traffic (this despite the lim- easy-to-use graphical user interface. A set of applications are itations from early 1990s as Italian and French Ministerial described and discussed including both operational applica- Decrees, IMO Assembly Resolutions, the institution of na- tions aimed at providing rapid responses to local oil spill tional and international marine protected areas and parks or emergences and managing applications aimed at mitigating the recognition by IMO of the Bonifacio Strait as the first the risk of oil spill impacts on the coast. Mediterranean Particularly Sensitive Sea Area in July 2011). Hazards crossing the Strait are due to the presence of hun- dreds of reefs, over seventy large or small islands, a strict eastern opening of about 6 km, and sea conditions that can 1 Introduction suddenly change due to large-scale evolving weather patterns, often associated with the topography of Corsica and The marine transport is one of the main sources of petroleum Sardinia that generates weather conditions often unexpected hydrocarbon in the Mediterranean Sea, crossed every year by and unpredictable, increasing the local maritime risk. De- about 220 000 vessels of more than 100 GRT (Gross Register tailed descriptions of the water circulation in the SoB and of Tonnage) each as estimated by the European Environmental the morphological features of the area can be found in Cucco Agency (EEA, 2006). These vessels approximately discharge et al. (2012) and in De Falco et al. (2011). 250 000 t of oil due to shipping operations such as deballast- Numerical modelling is a valid tool for the prediction of ing, tank washing, dry-docking, and fuel and oil discharges. oil spill movement and allows decision makers to promptly In addition, approximately 80 000 t of oil have been spilled respond to environmental crises. Many operational systems, between 1990–2005 from shipping accidents. Finally, acci- based on trajectories models linked to hydrodynamic and dents at oil terminals, together with routine discharges from

Published by Copernicus Publications on behalf of the European Geosciences Union. 444 A. Cucco et al.: Support of oil spill emergencies in the Bonifacio Strait

Figure 1 CORSICA Bonifacio strait La Maddalena Archipelago

STG

SARDINIA

Fig. 1. Geographical setting. meteorological ones, have been developed in order to anal- vide assistance in the prevention and/or limitation of dam- yse the dispersion of oil spill in European seas (e.g. Garcia ages and therefore the conservation of marine resources in and Flores, 1999; Brickman and Frank, 2000; Huggett et al., coastal waters, especially the most vulnerable areas of high 2003; Ferrer et al., 2004; Gonzales´ et al., 2008; Pinardi and environmental value typical of the Strait. Coppini, 2010). The description of the Bonifacio Oil Spill Operational These systems are generally not adequate in coastal wa- Model (BOOM hereafter) system and the evaluation of its ters as they use a fixed spatial resolution generally not lower accuracy in predicting both the surface transport and the then few kilometres (Chen et al., 2007). So, multiple nest- 3-D water circulation in the SoB is reported in Cucco et ing techniques to downscale the larger hydrodynamic model al. (2012). solutions are necessary to forecast sea currents and waves in In this paper, a detailed description of the model opera- the coastal area. In any case, these techniques must be over- tional usage and an overview of the main applications aimed come when simulated oil droplets leave the high resolution at supporting the response to local oil spills emergencies and restricted domain to enter into an extended domain (Wang et reducing the risk of environmental damage from oil spills in al., 2008). Unstructured grid models are a solution as they the coastal area are provided. allow both to reproduce the fluid motion and the oil slick transport processes over different spatial scales, and to adopt simplified nesting techniques to downscale the open ocean 2 The BOOM system model solutions to the coastal areas (Cucco et al., 2012). An approach of an oil spill prediction system for coastal The BOOM system is composed of a hierarchy of different areas, based on the use of operational finite element numeri- nested numerical forecasting models covering from basin to cal models, has been applied to the SoB (Fig. 1). coastal scale through a downscaling technique (Fig. 2). It is In 2009, an innovative forecasting system of the coastal based on both structured and unstructured grids aimed at pro- marine circulation was developed, using a numerical ap- viding a prognostic tool for managing oil spill emergencies in proach, within the framework of the European Integrated the Strait of Bonifacio. The system is fully detailed in Cucco project MyOcean and the Italian project SOS – Bonifacio. et al. (2012). In the following a brief summary of the adopted This system was developed in order to facilitate the rapid numerical models techniques are reported. planning and coordination of operations by the marine au- The coastal element of the system is composed of thorities to tackle pollution during oil spill emergencies. a set of finite element numerical models, including a The system allows users to obtain real time simulations to three-dimensional hydrodynamic model (SHYFEM3D; see predict the fate of different types of oil at sea and forecasts Umgiesser et al., 2004; Cucco and Umgiesser, 2006; Bajo et of their dispersal in the marine environment within a time al., 2007; Bellafiore et al., 2008; Cucco et al., 2012) coupled lag of 3 days. The main objective of this system is to pro- with a phase averaging wind-wave model (SHYFEM3D- WWM; see Roland et al., 2009; Ferrarin et al., 2008), and

Ocean Sci., 8, 443–454, 2012 www.ocean-sci.net/8/443/2012/ A. Cucco et al.: Support of oil spill emergencies in the Bonifacio Strait 445

BONIFACIO FORECASTING SYSTEM GUI ATMOSPHERIC FORCING Graphical User COAST GUARD HIGH RESOLUTION Interface COASTAL MODELS SHYFEM 3D – WWM SKIRON Oil spill & trajectory model WEB FEMOIL

ECMWF Data Assimilation air-sea coupling Analyses Sea Level Anomaly algorithms Sea Surface Temperature Downscaling Forecasts In situ temperature profile

WESTERN MED Mediterranean OGCM Boundary SUB-REGIONAL WEB NEMO (1o/16) Conditions FORECAST MODEL

Variational Initialization WEB

WEB VIFOP Data assimilation

OCEAN 3d-VAR Figure 2 OCEAN REGIONAL FORCING OCEAN SUB-REGIONAL FORCING

Fig. 2. Scheme of the whole system with different nested numerical forecasting models covering from basin to coastal scale, oceanographic and atmospheric. a Lagrangian trajectory module with a “weathering” module Atmospheric conditions for the coastal component are pro- (FEMOIL, see Cucco et al., 2012) offline coupled with the vided by the very high resolution meteorological forecast- SHYFEM3D-WWM. ing system named SKIRON, developed by the University of Such numerical models are aimed at operationally repro- Athens (Kallos et al., 1997; Kallos and Pytharoulis, 2005), ducing the hydrodynamics and transport processes in a re- while for the sub-regional component the forecasting system stricted domain corresponding to the Bonifacio Strait area. developed by the MyOcean key-user ECMWF. The domain has been reproduced by means of adaptive mesh The BOOM system currently produces, daily and opera- generator onto a finite element grid composed by 33 563 tionally since the end of 2010, a 3-days forecast of wind and nodes and 64 292 elements (see Fig. 3 in Cucco et al., 2012). wave fields, 3-D water circulation, temperature, salinity and The coastal system is nested to a sub-regional ocean fore- of the fate of the oil slick at sea in the Bonifacio area. A casting system applied to the western Mediterranean Sea and graphical user interface (GUI; Ribotti et al., 2012) provides a named WMED (Sorgente et al., 2011). WMED, based on user-friendly accessibility, usability and interaction with the the Princeton Ocean Model (Blumberg and Mellor, 1987; BOOM system by setting up scenarios, running simulations Mellor, 1991), is a three-dimensional model covering part of and analyzing the produced consequences of an oil spill. the western Mediterranean area, between 3◦ E and 16.5◦ E. It uses a uniform horizontal orthogonal grid with a resolution of 1/32◦ (about 3.5 km) in longitude and latitude while 3 The operational usage vertically it is discretized by 30 sigma levels. At its lateral The forecasting system based on the SHYFEM3D-WWM open boundaries it is nested with daily mean fields com- produces daily and operationally the datasets needed by puted by the MyOcean-OPA regional model for the whole FEMOIL to forecast the fate of the oil spill. In this para- Mediterranean Sea, with a horizontal resolution of 1/16◦ im- graph a description of the BOOM operational setup is re- plemented at INGV in Bologna (Tonani et al., 2009). ported. Furthermore, the accessibility to FEMOIL through- The SHYFEM3D is nested to the WMED through an out the GUI and its usage for providing a prediction of the oil interface for managing forcing and boundary data in real spill fate in both forward and backward mode are described. time, which allows receiving daily both high resolution atmospheric and hydrological data along the domain boundaries for the following 3 days.

www.ocean-sci.net/8/443/2012/ Ocean Sci., 8, 443–454, 2012 Figure 3 446 A. Cucco et al.: Support of oil spill emergencies in the Bonifacio Strait

Fig. 3. The BOOM forecasting chain.

3.1 The model forecasting chain The results obtained by the SHYFEM3D-WWM numerical simulation are made available daily on www.seaforecast. Wind data fields from SKIRON forecasting atmospheric cnr.it in the form of snapshots of the surface currents inten- model, water levels time series and interpolated T, S fields sity and direction and of the wind wave significant height and from WMED regional ocean model are provided daily to the propagation direction is computed every 6 h for the next 72 h SHYFEM3D-WWM. All the forcing datasets regard 5-days forward (from t0 to t+3). forecasting simulations. Then daily, a 5-day hydrodynamic and wind wave model run for the SoB area is performed. The integration time step 3.2 Forward and backward analysis of the flow module SHYFEM3D was set to be variable and top limited by a Courant number threshold equal to 0.8. On the other hand, for the wave simulations, the time step was The simulations of the oil spill fate were initialized, set up set to be fixed and equal to 300 s. Synchronization between and run using a graphical user interface communicating with the two processes is guaranteed by the coupling scheme. the FEMOIL. The GUI is a software tool, written in Java A warm start procedure was implemented to avoid the use programming language, that makes it easy for a user to create of an additional spin-up time needed when model variables simulations of oil-spill emergencies. In particular, it allows a initialization is made with homogeneous or non realistic spa- user to interact directly with the FEMOIL through a set of interactive panels. tial distribution. Simulation starting time (t0) and ending time The GUI guides the user through the creation of an oil spill (t+5) respectively correspond to the 00:00 of the present day and to 00:00 of the 5th day forward respectively (Fig. 3). scenario, launching a simulation and analysis of the results The computational time demand is variable and depending generated. on the values of the flow model time steps. On average, it was The user specifies the emergency scenario by using a con- estimated to be about 2.5 h when computation is carried out trol panel, composed of a series of user friendly sub-panels on a 4 Intel Core 2 Quad CPUs of a 3.00 GHz workstation. which allow selection of: the date and hour of the last de- At the end of the model run, the computed surface water tection of the oil spill between the time t−1 and t+1; the ge- current, wave drift, wind speed and surface T fields are saved ographical location of the last detection of the oil spill; the to an external file. The dataset is organized to include data direction of integration, if forward or backward; the amount and type of oil spilled; the mode of spilling, if instantaneous starting from the time t−1, corresponding to 00:00 of the 1st or continuous; the output data location and to launch the day backward to the time t5 with a temporal frequency of 1/300 s. Finally, a further procedure is carried out to obtain FEMOIL model run. a dataset of water current, wave drift and wind speed vector Results generated by the numerical simulation are stored fields with both inverse temporal sequence and inverted vec- in an archive selected by the user and displayed in the form of animations and snapshots. In the case of forward run, results tor directions and starting from the time t+1, corresponding consist of the trajectories and the density of the oil dispersed to 00:00 of the 1st day, forward to the time t−4, corresponding to time 00:00 of the 4th day backward. The data needed at sea, with the impacted parts of coast highlighted on the to generate the datasets corresponding to the past days from map. In the case of a backward run, results include only the tra- t−1 to t−4 are provided by the previous days operational simulations. These two sets of external files constitute the two jectory followed backward in time by the oil spill. No weath- forcing datasets needed to run the off-line FEMOIL module ering processes and oil stranding at coast are included in the both in forward and in backward mode (Fig. 3). backward simulation. Both advection and diffusion processes are taken into account in the backward mode in order to simulate both the

Ocean Sci., 8, 443–454, 2012 www.ocean-sci.net/8/443/2012/ A. Cucco et al.: Support of oil spill emergencies in the Bonifacio Strait 447 mean trajectory followed back in time and the area of possi- tracking back in time the probable path followed by the oil ble location of the pollutant source. dispersed in the water. The system allows to run the simulation of the oil spill The method consists of performing a sequential run of 2 fate even if the dataset by the daily SHYFEM3D-WWM op- simulations, one “forward” and the other “backward”. In the erational model simulation is still not ready. In this case, the forward run, the hydrodynamic and wave models reproduce input dataset of the day before is used instead, adjusting the the water circulation and wave field in a selected period (DT) reference t0 to the time t+1, therefore partially remedying to before the time (TF) when the oil slick has been detected in the delay in the generation of the updated prediction. its final position (XF). The obtained results are stored in external files and processed in order to invert both the temporal order of the fields sequence and the direction of current and 4 Applications wave propagation. The “backward” run is then performed and the Lagrangian advection model used to transport and The system has been used to provide support to local author- diffuse a quantity of particles representing the amount of oil ity during emergencies due to oil spill accident occurred in spill detected in the final position XF at time TF. The sim- the SoB. Furthermore, a set of scenarios analyses was per- ulation runs to a time corresponding to DT using, as input, formed to evaluate in advance the risk induced by hypo- the stored and processed current and wave data. Therefore, thetical impacts of hydrocarbons in the coastal areas of the the obtained results provide a tracking of the detected oil Bonifacio Strait. The results of these activities have been in- spill from the moment TF and the final position XF, back cluded in the “Local emergency operations plan against main time to TI = TF − DT and to the initial most probable po- rine pollution by oil and other harmful substances” of the sition (XI). Coast Guard at La Maddalena. This plan is activated on the An example of a backward analysis carried out to back- basis of art. 11 of the Italian Law 979/82 of the “Regulations track a fuel oil slick of about 30 m3 detected in XF at noon of for the protection of the sea” in case of pollution or imminent the 27 August 2008 is shown in Fig. 4. The first frame refers threat of pollution of the sea caused by dumping, accidental to time TF, whereas the last to time TI, 6 days before, then event of oil or other harmful substances. 21 August. At time TI the position of the slick is located on In the following, the results obtained by the application the main maritime traffic route (XI), where the release prob- of the system during two different oil spill emergencies are ably occurred. In particular, for the simulated event, compar- reported and discussed. Finally, the results obtained by a se- ison between the numerical results and traffic data reveals lected simulated scenario and risk analyses are reported. that the hydrocarbon spill detected on 27 August was probably generated in the recommended route area, corresponding 4.1 Response to emergency to the position XI. During this period, 21 transits of Ro/Pax, In this sub-section, two different examples of applications of Ro/Ro ships, cargos and cruise ships through the Strait are the BOOM system as a response to oil spill emergencies are recorded. Furthermore, considering the kind of ship and their reported. In the first case, the system was applied to back- routes, the number of those possibly responsible can be re- track the trajectory followed by an oil slick detected in the duced to 15 vessels, therefore increasing the probability of SoB, in order to individuate the potential source of pollution. its identification. In the second case, the system was used to predict the trajectory followed by the oil released in the water during an 4.1.2 Forward investigation accident that occurred in the SoB. The system simulation has been qualitatively verified in early 4.1.1 Backward investigation January 2011 during a case study when an oil spill occurred in the harbour of Porto Torres (PT), north-western Sardinia. When accidents occur that lead to large oil spills, national During the operation of oil transfer from a ship tanker at authorities are usually quick to respond and identify those re- the off-shore pipe station in front of PT harbour, about 50 m3 sponsible. Nevertheless, most of the “small” oil spill events of heavy crude oil (API 19.7◦) were released into the sea. are caused by the common illegal practice of refuelling or The oil spilled out continuously for about 18 h, starting from pumping oily bilge water overboard. Even if they constitute 10 January 2011 at the 10:18 p.m. of local time. small spills, their intense frequency can have significant neg- The slick moved north-eastward for about 5-days, inter- ative effects on the marine environment. In these cases, iden- secting the coast at several locations between the villages tification and quantification of the responsibles is very diffi- of PT and Santa Teresa di Gallura (Fig. 5). On 17 January cult and often quite impossible. at 12:00 a.m. LT, 7 days after the accident, an oil spill was In order to provide support to the local Italian Coast Guard found during an air survey in the coastal waters at the en- for detecting the responsibilities for such events, a numerical trance of the Bonifacio Strait (Fig. 5). The local authority, tool for carrying out the so-called “backward investigation” in order to verify the connection between the pollutant and was developed. The system, based on the BOOM, aims at the PT accident and to exclude further sources of spills in www.ocean-sci.net/8/443/2012/ Ocean Sci., 8, 443–454, 2012 448 A. Cucco et al.: Support of oil spill emergencies in the Bonifacio Strait

Figure 4

Fig. 4. Results of the backward investigation: XF and XI are the final and the most probable initial positions of the oil slick respectively at time TF (27 August 2008 at 06:00 a.m.) and at time TI, which corresponds to 6 days before TF (21 August 2008 at 06:00 a.m.). The areas between the blue dashed lines correspond to the maritime traffic route through the Strait of Bonifacio. the area (e.g. tanks cleaning bilge waters), ran the BOOM in produce the local bathymetric and morphodynamic features backward mode. The obtained results revealed that the prove- (Fig. 6). A 9-day simulation run was performed, releasing the nience of the spilled oil was from the PT area. Samples of oil in continuous mode for about 20 h starting from 10 Jan- floating oil were successively collected and chemically ana- uary at 10:00 p.m. The atmospheric field produced from SK- lyzed in the laboratory, certifying its origin from PT. IRON for the first day of prediction was used to force the Subsequently a new simulation was carried out to verify model domain. The model was initialized with water levels the model capability in reproducing the fate of the occurred and current speeds generated by the BOOM system and open spill in forward mode. The model domain was extended to boundary data from WMED were used. the interested area, increasing the mesh resolution to re-

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Bonifacio Strait Bonifacio Strait

SANTA TERESA DI BEACHED OIL GALLURA 17-01-2011

forecasted oil trajectory

Fig. 5. Map of the area where the accident of Porto Torres occurred in JanuaryFigure 20115 and the hindcast simulation results. Red lines indicate tracts of coastal area impacted by the simulated oil; green lines the sampled beached oil. The blue circle indicates where the oil at sea was detected by airborne surveys close to the entrance of the Bonifacio Strait. In the left panel the black line indicates the average trajectory followed by the particles on water. In the right panel a snapshot of model results at the 12:00 a.m. of 17 January 2011.

The model reproduced fairly well the probable trajectory followed by the spilled oil during the whole period. This is evidenced by the position of the oil particles beached on the shore, which mainly corresponds to the coastal area impacted by the pollutants during the event, as reported in Fig. 5. Fur- thermore, the model was able to reproduce the fate of the oil in water, simulating the presence of oil particles on water at the entrance of the Strait during the 7 days after the released time at PT location, in agreement with the experimental evi- dence.

4.2 Hazard mitigation

In this sub-section two different types of applications aimed at mitigating the risk of environmental damage due to impact of oil spills in the coastal area are reported. In the first case, the system was used to produce, by means of ad hoc scenar- Fig. 6. The extended model domain. In red and blue the sampled ios analysis, essential information aimed at preventing the oil beached oil. spill impacts on the coast. In the second case, the system was applied to individuate in advance, by means of ad hoc risk analysis, the traits of coast more subjected to the potential area and the type and amount of hydrocarbons released. For impacts of oil spills. each macro-scenario, eight simulations are carried out in order to consider the seasonal variability of wind regime and 4.2.1 Scenarios analysis water temperature. For all the simulations, stationary open boundary conditions and wind forcing are defined and a spin- A series of numerical simulations was carried out in order up time of 3 days is selected to eliminate the noise gener- to reproduce the most probable pollutant scenarios, and the ated by the imposed initial conditions. Wind-wave propaga- areas with the highest risk of accident, affecting the Strait tion and the 3-D water circulation is reproduced for the Strait of Bonifacio. These scenarios have been chosen consider- area. For each considered macro-scenario, a defined quan- ing local climate condition, maritime traffic and historical tity of numerical particles are initialised in the selected area maritime emergency records for the last 16 years. Six main of the oil spill. Each particle represents a quantity of oil re- macro-scenarios have been defined, differing by the spilling leased in the water with an associated density, depending on www.ocean-sci.net/8/443/2012/ Ocean Sci., 8, 443–454, 2012 Figure 7 450 A. Cucco et al.: Support of oil spill emergencies in the Bonifacio Strait

Fig. 7. Surface current speed and significant wave height induced by a 13 m s−1 Mistral wind in the Bonifacio Strait and La Maddalena archipelago area. the type of oil considered. The amount of oil released varies hours after the release, all the particles reach the coast, par- between 10 000 kg and 100 kg, and oil density is representa- ticularly around the islands of La Maddalena and Caprera tive of fuel oil, marine diesel and crude oil. (see green dots in Fig. 8). About 50 scenarios are considered and the following re- The temporal variation in the total amount of oil, split sults are obtained: between quantity still in the water and quantity beached, is shown in Fig. 9. The oil mass dispersed in the water (green – wave and surface current velocity fields; close symbols curve) quickly decreases during the first 3– – hourly field of oil slick depth; 4 h due to high evaporative processes. After this period, the recorded reduction is due to the oil reaching the coast, as – hourly field of Lagrangian particle position and im- shown by the increase in the green curve. After the beaching, pacted areas on shore; the total quantity is still diminishing due to evaporative and emulsification processes occurring on the oil that re-enters – time series of oil quantity dispersed at sea or beached. the sea due to the wind-wave impacts on the shore. Here we show the results obtained for a scenario simulating a real accident with hydrocarbon spillage that occurred in 4.2.2 Risk analysis 1994, involving the French ferry Montestello, on the route Livorno–Barcelona, run aground inside the La Maddalena The BOOM system has been used to produce probabilistic Archipelago during a strong Mistral wind storm. The sim- estimates of the oil impact on the coast as a function of oil ulated accident is set in the same period and with the same type. Three different kind of accidents are considered involv- original weather conditions and an initial spill of 30 m3 of ing an oil-tank vessel, a cruise-ship and a ferry boat, and the fuel oil. The surface water circulation and the wind wave quantity of oil contained in the bunkers of each of the three field computed by the model are shown in Fig. 7. The strong vessels. Mistral wind (13 m s−1) generates an eastward water circula- For each category, a one-year simulation is carried out, tion with current velocities reaching about 1 m s−1. The wind forcing the hydrodynamic and wave model with wind and induced wave field is moved south-easterly with a significant open boundary data provided by the meteorological and the wave height (HS) decreasing eastward. Maximum values of oceanographic models. Each simulation is initialised with an significant wave height (HS) reaching 3 m are found outside amount of particles statistically sufficient to cover the paths the Strait, while inside the La Maddalena Archipelago the corresponding to the maritime traffic routes followed by the HS is always less than 0.8 m. considered ship categories crossing the Strait. The Lagrangian particles released are quickly transported The “seeding” of particles is repeated daily in order to eastward due to the combined effect of wave, water currents take into account the influence of the meteorological vari- and wind drift. Six snapshots, illustrating the computed par- ability on the Lagrangian transport. Each particle represents ticles distribution in the water, are shown in Fig. 8. Seven a possible spill event of a defined quantity and type of oil,

Ocean Sci., 8, 443–454, 2012 www.ocean-sci.net/8/443/2012/ A. Cucco et al.: Support of oil spill emergencies in theFigure Bonifacio 8 Strait 451

0 hrs 1 hr 2 hrs

3 hrs 4 hrs 5 hrs

Fig. 8. Snapshots of oil particles distribution dispersed in the waterFigure (red dots)9 and beached on the shore (green dots).

Fig. 9. Temporal variation of the total amount of oil quantity dispersed in the water column (green close symbols curve) and beached on the shore (red curve). which could occur anywhere along the whole maritime route the distribution of a relative risk index which ranges between and at any time of the year. The computed water currents, 0 and 1 are produced. wave propagation and wind drift transported all the particles The derived risk index aims at describing, in a probabilistic within the numerical domain. Each particle is also inﬂuenced way, the risk of oil spilled reaching the coast, as a function of by weathering and stranding processes, leading to a reduction a geophysical forcing only. Neither vulnerability aspects (bi- in the quantity of oil at sea. ological resources, environmental values, anthropic values, At the end of each model run, the quantity and the num- etc.) nor accessibility of the coast have been considered. ber of oil particles beached on the coast are computed. The As an example, the yearly map of risk induced by the im- coastline is divided in 200 m cells and, for each cell, the total pact of oil on the coast, as released by cruise ships travel- amount of oil beached during each month of the simulated ling through the Bonifacio Strait, is reported in Fig. 10. The year is calculated. The cell values are then normalized to the maximum risk of impact is found along almost the whole maximum quantity of oil beached on a cell during the con- length of the channel between Sardinia and the La Mad- sidered month and, for each category, 12 maps consisting on dalena Archipelago. www.ocean-sci.net/8/443/2012/ Ocean Sci., 8, 443–454, 2012 452 A. Cucco et al.: Support of oil spill emergencies in the Bonifacio Strait

Fig. 10. Risk map of oil impact on the coast as consequence of a potential release from cruise-ships.

5 Conclusions Currently the system produces, daily and operationally, a 3-day forecast of wind and wave fields, 3-D water circula- The BOOM represents an innovative operational system de- tion, temperature and salinity for the area of interest. Fur- veloped to provide support to the Italian Coast Guard in man- thermore, it has been used to investigate the consequences aging oil-spill emergencies in the coastal area of the Strait of of oil-spill events, to produce risk maps identifying the most Bonifacio. exposed areas to the risk of oil impact in relation to both pe- This is an integrated numerical tool whose coastal core is riod of the year and type and quantity of spilled oil, and as organized in a set of fully coupled high resolution numeri- a tool for tracking back the surface trajectories of oil slicks. cal models based on the finite element method. The models The operational validation of the system was realised in Jan- include a 3-D hydrodynamics model, a wind-wave model, uary 2011 when an oil spill occurred from the harbour of a Lagrangian trajectory model and a module for reproduc- Porto Torres. The results of the simulations were well com- ing the main weathering processes impacting the oil slick. parable with beached oil and with oil slick positions at sea, BOOM has been fully operational and utilized since the end giving valuable information to the Coast Guard on their ori- of 2010 by the Italian Coast Guard in La Maddalena island gin and on the area affected by the accident. (Sardinia, Italy), realized within the frameworks of the Ital- Simulation results of oil spill scenarios can provide the ian project “SOS-Bonifacio” and the European project My- local Coast Guard with information on the fate of oil spills Ocean. The system allows, through the interaction with an and those most probable in the area. In particular, the hourly easy-to-use GUI, the user to operationally forecast the fate maps of oil slick position and those showing which areas of oil spills in the whole area of the Bonifacio Strait and La would be most probably impacted, as a function of differ- Maddalena Archipelago. ent meteorological conditions, provide a useful tool to im- The innovative approach consists of the use of operational prove the management of oil spill emergencies at sea. For finite elements numerical models with a spatial resolution up these reasons, the local Coast Guard in La Maddalena has to 10 m, fully nested with an open ocean operational model inserted the simulated scenarios in its “Local anti-pollution based on the finite differences method (WMED) to reproduce plan for 2009” requested by the Italian Ministry for Environ- the transport processes occurring in coastal areas character- ment. These simulations will be used to predict in advance ized by a complicated geometry. the trajectory of the oil, then permitting decision makers to

Ocean Sci., 8, 443–454, 2012 www.ocean-sci.net/8/443/2012/ A. Cucco et al.: Support of oil spill emergencies in the Bonifacio Strait 453 plan the optimal remedial action for minimizing oil pollution Cucco, A. and Umgiesser, G.: Modeling the Venice Lagoon resi- and reducing time response and costs. dence time, Ecological Modelling, 193, 34–51, 2006. Further information is also provided by the risk analysis, Cucco, A., Sinerchia, M., Ribotti, A., Olita, A., Fazioli, L., Sor- which allows the local Coast Guard to identify the most ex- gente, B., Perilli A., Borghini, M., Schroeder, K., and Sorgente, posed areas to the risk of oil spill impact during the year. This R.: A high resolution real time forecasting system for predicting is also useful for the identification of the most suitable areas the fate of oil spills in the Strait of Bonifacio (western Mediter- ranean), Mari. Poll. Bull., 64, 6, 1186–1200, 2012. where instruments and resources should be concentrated. De Falco, G., De Muro, S., Batzella, T., and Cucco, A.: Carbonate Finally, even if the backward investigation cannot exactly sedimentation and hydrodynamic pattern on a modern temperate pinpoint the initial position of the oil spill, it still provides shelf: The strait of Bonifacio (western Mediterranean), Estuar. information on the most probable path followed by the oil Coast. Shelf Sci., 93, 14–26, 2011. slick since its detection. EEA (European Environment Agency): Priority issues in the The tools described above define the BOOM as a useful in- Mediterranean environment, EEA Report no. 4, 88 pp., 2006. strument for any local Coast Guard in the management of oil Ferrarin, C. F., Umgiesser, G., Cucco, A., Hsu, T.-W., Roland, A., spill events in coastal areas like those of the Bonifacio Strait and Amos, C. 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